Filters used to clean air include filters for internal filtration and filters for surface filtration, and dust collectors use the filters for surface filtration. In surface filtration, dust is collected on the surface of a filter, to form a dust layer on the surface of the filter, and dust is successively collected by the dust layer. When the dust layer grows to a certain thickness, the dust layer is removed from the surface of the filter by air pressure, and the operation to form a dust layer on the surface of the filter is repeated again.
The fibers constituting the filters used to filter high temperature exhaust gases emitted from refuse incinerators, coal boilers, metal blast furnaces and the like include polyphenylene sulfide (hereinafter abbreviated as PPS) fibers, meta-aramid fibers, fluorine-based fibers, polyimide fibers and the like, respectively, excellent in heat resistance and chemical resistance, and they are formed into nonwoven fabrics to be used as filters. Among them, PPS fibers are excellent in hydrolytic resistance, acid resistance, and alkali resistance, and widely used as bag filters for dust collection of coal boilers.
For a bag filter, good dust release performance and dust collection performance are required as filter performance. When the dust release performance is inferior, a problem that the bag filter is clogged with dust occurs, which raises the pressure loss of the dust collector. In addition, a bag filter excellent in dust collection performance is required to reduce the dust concentration in exhaust gases.
JP 2010-264430 A proposes a filter cloth (filter) that has a two-layer structure of a dust collecting layer and a strength maintaining layer and uses a nonwoven fabric meltblown with PPS as the dust collecting layer. JP H10-165729 A proposes a filter cloth (filter) in which PPS fibers having a single fiber fineness of 1.8 d (2.0 dtex) or less are arranged in a surface layer. JP 2011-5860 A proposes a filter that has at least two layers of webs, in which the web on the air inflow surface side is made of heat resistant fibers having a fiber diameter of 15 μm or less, and the web on the air discharge surface side is made of heat resistant fibers having a fiber diameter of 20 μm or more.
Although the filter cloth (filter) of JP '430 certainly provides good dust release performance and dust collection performance, each step of needle punching, meltblowing, and water jet punching is necessary for production, and can be produced only by specific equipment. In addition to this, there has been a problem of high cost.
Although the method of JP '729 is certainly good in dust release performance and dust collection performance, it has insufficient stiffness and abrasion resistance at high temperatures, so there has been such a problem that the filter cloth (filter) is broken due to the progress of physical deterioration during use.
Although the method of JP '860 certainly makes stiffness and abrasion resistance of the filter good, since thick fiber diameter fibers on the air discharge surface side of the filter are entangled into the air inflow surface side, there has been a problem that sufficient dust release performance or dust collection performance cannot be obtained.
Accordingly, it could be helpful to provide a laminated polyarylene sulfide heat-resistant filter excellent in stiffness and abrasion resistance at high temperatures while having excellent dust release performance and dust collection performance inexpensively (at a low cost).